The fundamental technology of cinema film projection largely has remained unchanged for over one hundred years. A filmstrip containing a series of images is passed through a powerful light beam at 24 frames per second. The light passing through the filmstrip is shuttered twice to produce two images of each frame. After each image is shuttered twice, the film is advanced to the next image and the shuttering repeated. The result is a 48 Hz image sequence produced by a 24 frame per second source. While this produces a pleasing image while limiting the amount of film used to produce a movie, the frame rate is insufficient to eliminate flicker during bright image sequences.
Recently, new technologies have emerged to challenge film distribution and projection. These new technologies use micromirror or liquid crystal spatial light modulators to spatially modulate light using digitized image data. In many cases, these technologies provide superior image quality while greatly reducing film distribution costs and eliminating the image degradation that occurs due to the wear and tear associated with traditional film projection.
Some of these new technologies operate digitally—that is, each pixel of the modulator is either on or off, fully illuminating, or not illuminating, a corresponding image pixel. Digital modulators produce gray scale images by temporally alternating between the on and off states and using a receptor such as the human eye to integrate the light received from each pixel over a given time. In a similar manner, some display systems sequentially produce three single color images which are combined by the viewer to achieve the perception of a three-color image.
One of the difficulties encountered using digital spatial light modulators is the provision of sufficient bit depth. Images digitized to bit resolutions of only 8 or 9 bits per color per pixel can produce false contouring artifacts—perceived as display regions having a constant intensity with a sharp change in intensity to the next region, instead of the intended gradually changing intensity through the various regions. These objectionable contouring artifacts can be eliminated by increasing the number of data bits used to represent each pixel. Unfortunately, increasing the number of image bits increases the necessary system bandwidth. Furthermore, the least significant bits (LSBs) of the image have such short display times that the system cannot load the next bit of data into to modulator during the bit display period.
The display period for each bit also depends on the frame rate of the display. Slower frame rates allow longer frame periods and enable greater bit depths. The slower frame rates, however, are prone to flickering. Higher frame rates eliminate flicker, but limit the bit depth of the image since the display time of the LSBs becomes shorter than the modulator load time. What is needed is a method and system that allows both a high frame rate to eliminate flicker, and sufficiently long data display periods.